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Q & A: being and nothingness again

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Most recent answer: 08/23/2009
Q:
How can space be deformed to create gravity if its a perfect void. Doesnt this reaction mean that its something rather than nothing. I dont know how else to phrase this I hope this makes sense. It seems counter intuitive that we are looking for mystery "dark matter & energy" could these not be properties of "empty space" itself. Akin to our ancestors thinking of wind as "dark energy".
- Chad (age 34)
Asheboro, NC, USA
A:
Tough questions. Since space plays a much more active role in General Relativity than in Newtonian physics, it's tempting to say it's 'something'. There's no particular reason to resist the temptation, although giving in to it doesn't really tell you anything new.

"Dark matter' is, so far as we know now, just a set of particles which happen not to have any strong interactions except gravity with our type of particles. It does clump up in galaxies. It's not really a philosophical issue, just a hard thing to get at experimentally.


"Dark energy' may be nothing but an inherent aspect of the behavior of 'empty space', as you say. However, there are strong reasons to think this behavior was once different. There are also theoretical reasons to think that there can be a variety of different 'empty' spaces, with different densities of dark energy. So there's something to study. It does support your point about not treating space as mere nothingness.

Mike W.

(published on 08/20/2009)

Follow-Up #1: accelerating expansion

Q:
If dark energy were to be an inherent property of space/time itself, and this property repulsive, wouldn't it make more sense of the expanding universe? As more space builds the more the repulsion builds resulting in an expanding universe building on itself and getting faster. It would also seem to affect gravity as well? (space pushing, rather than matter pulling)
- Chad (age 34)
Asheboro, NC, USA
A:
You've pretty much described the modern picture, in which an acceleration of the  expansion is driven by a repulsion built in to spacetime. The expansion does indeed 'build on itself', or, to put the same thought mathematically, it's exponential.

However, the universe was expanding for a long time (about 10 billion years) before this tendency to accelerate became important. Up to that point, the density of mass in the universe was high enough to slow the expansion. So whatever might ultimately explain the expansion of the universe, it's not the current dark energy, which is just recently starting to have a noticeable effect.

We don't know whether the current dark energy is 'inherent' in any spacetime or a particular property of one version of spacetime. If it's the latter, it may someday change as spacetime settles into a different state. The standard inflationary picture claims that a very rapid very early exponential expansion stopped when the universe settled into something like its current state.

Mike W.

(published on 08/23/2009)

Follow-up on this answer.